Transmission, hybrid drive train, and drive train for an electric vehicle

ABSTRACT

A transmission includes a main gear set, an auxiliary gear set and an electric motor with a rotor and a stator. A third shaft of the main gear set is connected to a transmission output shaft. A second shaft of the auxiliary gear set is connectable through a first auxiliary shift element to a first shaft of the main gear set and through a second auxiliary shift element to the third shaft of the main gear set or to a fourth shaft of the main gear set. A third shaft of the auxiliary gear set is constantly connected to a second shaft of the main gear set. A first shaft of the auxiliary gear set is constantly connected to the rotor.

FIELD OF THE INVENTION

The invention relates generally to a transmission with a transmissioninput shaft and a transmission output shaft, a main gear set, anauxiliary gear set, and an electric motor with a rotor and a stator. Theinvention also relates generally to a drive train for a motor vehiclewith a transmission.

BACKGROUND

Herein, a transmission in particular designates a multi-speedtransmission, with which a predetermined number of gears, thus fixedtransmission ratio relationships between a transmission input shaft andthe transmission output shaft, are automatically shiftable by shiftelements. Herein, the shift elements comprise, for example, clutches orbrakes. Such transmissions are primarily used in automotiveapplications, in order to adjust the rotational speed and torque outputcapabilities of the drive unit to the driving resistance of the motorvehicle in a suitable manner.

From patent application DE 10 2012 201 377 A1 of the applicant, atransmission with a transmission input shaft and a transmission outputshaft, and two power paths between the transmission input shaft and amain gear set with two individual planetary gear sets, with four shaftsdesignated in the order of rotational speeds as the first, second, thirdand fourth shafts is known, whereas the third of the four shafts isconnected to the transmission output shaft. An electric motor isconnected through a planetary transmission at the first shaft of themain gear set.

SUMMARY OF THE INVENTION

Exemplary aspects of the invention assist to improve the load-shiftingbehavior of a transmission.

Additional exemplary aspects of the invention assist to improve theoperating range of the transmission, such that, in any gear, theelectric motor is able to receive mechanical power from the transmissionoutput shaft or deliver power to it.

The transmission comprises at least one transmission input shaft and atransmission output shaft, a main gear set, an auxiliary gear set, andan electric motor with a rotor and a stator.

The main gear set features a first and a second planetary gear set witha total of four shafts designated in the order of rotational speeds asthe first, second, third and fourth shafts. The main gear set is thusformed as a two-carrier/four-shaft transmission. The auxiliary gear setfeatures a planetary gear set with a total of three shafts designated asthe first, second and third shafts.

The first shaft of the auxiliary gear set is constantly connected to therotor. The third shaft of the main gear set is connected to thetransmission output shaft.

A “two-carrier/four-shaft transmission” is understood to be a planetarytransmission that is formed from two individual planetary gear setskinematically coupled with each other through exactly two couplingshafts, and with which four of its elements (“shafts”) are freelyaccessible for other transmission elements. Thereby, a coupling shaft isdefined as a constant mechanical connection between one element—thus, asun gear or a carrier or a ring gear—of the first individual planetarygear set with one element—thus, a sun gear or a carrier or a ringgear—of the second individual planetary gear set. The number ofindividual planetary gear sets and the number of free shafts are notdefined by the visual appearance of the transmission, but through itskinematics. In each gear of a two-carrier/four-shaft transmission, twoof the shift elements of the transmission connected to elements of thetwo-carrier/four-shaft transmission must be locked. For the graphicalrepresentation of the kinematics of the transmission, a rotational speeddiagram of the transmission (for example, the Kutzbach diagram knownfrom transmission theory) is typically used. Known embodiments of such atwo-carrier/four-shaft transmission include the so-called “Ravigneauxgear set” and the so-called “Simpson gear set.”

A reduced two-carrier/four-shaft transmission is a structural shape of atwo-carrier/four-shaft transmission in which one element—that is, a sungear, a carrier or a ring—of the transmission is spared, since anotherelement of the transmission takes over its task, without therebychanging the kinematics. That element that takes over the function ofthe spared element is thus one of the coupling shafts of thetransmission at the same time. A known embodiment of this is theRavigneaux gear set, which features either two sun gears and only onering gear, or two ring gears and only one sun gear.

Through at least one power path, the transmission input shaft isconnectable through at least one shift element to at least one of thefour shafts of the main gear set. In a preferred exemplary embodiment,the at least one power path is connectable through two shift elements totwo of the four shafts of the main gear set. By locking one of the shiftelements, a torque-proof connection between the at least one power pathand one of the four shafts of the main gear set is thus established, bywhich torque can be led from the transmission input shaft to the maingear set. “At least one power path” is to be understood such that thetransmission features one or more power paths between the transmissioninput shaft and the main gear set.

Upon use of a motor vehicle, the transmission input shaft is connectableto a shaft of a drive unit, or is connectable through a clutch, suchthat mechanical power of the drive unit can be supplied to thetransmission input shaft. The drive unit may be formed as an internalcombustion engine and as an electric motor. The transmission outputshaft serves as an interface for transferring mechanical power to thedrive wheels of the motor vehicle.

In the following, a “shaft” is not solely understood as, for example, acylindrical, rotatably mounted machine element for the transfer oftorques, but is also understood as a general connection element, whichconnects individual components or elements to each other, in particularconnection elements that connect several elements to each other in atorque-proof manner.

A planetary gear set comprises a sun gear, a carrier and a ring gear.Planetary gears, which mesh with the toothing of the sun gear and/orwith the toothing of the ring gear, are rotatably mounted on thecarrier. In the following, a negative gear set describes a planetarygear set with a carrier, on which the planetary gears are rotatablymounted, with a sun gear and a ring gear, whereas the toothing of atleast one of one of the planetary gears meshes both with the toothing ofthe sun gear and with the toothing of the ring gear, by which the ringgear and the sun gear rotate in opposite directions of rotation, if thesun gear rotates with a fixed carrier.

Both sun gear and ring gear of a planetary gear set can also be dividedinto several segments. For example, it is conceivable that the planetgears mesh with two sun gears, which are not connected to each other. Ofcourse, the rotational speed relationships are identical on bothsegments of the sun gear, as if they were connected to each other.

A positive gear set differs from the negative planetary gear set justdescribed in that the positive gear set features inner and outerplanetary gears, which are rotatably mounted on the carrier. Thereby,the toothing of the inner planetary gears meshes, on the one hand, withthe toothing of the sun gear and, on the other hand, with the toothingof the outer planetary gears. In addition, the toothing of the outerplanetary gears meshes with the toothing of the ring gear. This has theconsequence that, with a fixed carrier, the ring gear and the sun gearrotate in the same direction of rotation.

The stationary transmission ratio defines the rotational speedrelationship between the sun gear and ring gear of a planetary gear setwith a torque-proof carrier. Since, with a negative gear set, thedirection of rotation between the sun gear and ring gear with atorque-proof carrier is reversed, the stationary transmission ratioalways increases to a negative value with a negative gear set.

In the rotational speed diagram, the rotational speed relationships ofthe individual shafts are plotted in a vertical direction. Thehorizontal gaps between the shafts arise from the transmission ratiorelationships between the shafts, such that rotational speedrelationships and torque relationships of the shafts pertaining to agiven operating point can be connected by a straight line. Thetransmission ratio relationships between the shafts arise from thestationary transmission ratios of the planetary gear sets involved. Therotational speed diagram can be presented, for example, in the form of aKutzbach diagram.

Four shafts designated in the order of rotational speeds as the first,second, third and fourth shafts are characterized in that the rotationalspeeds of such shafts in the specified sequence increase, decrease orare equal in a linear manner. In other words, the rotational speed ofthe first shaft is less than or equal to the rotational speed of thesecond shaft. In turn, the rotational speed of the second shaft is lessthan or equal to the rotational speed of the third shaft. The rotationalspeed of the third shaft is less than or equal to the rotational speedof the fourth shaft. This sequence is also reversible, such that thefourth shaft features the highest speed, while the first shaft assumes arotational speed that is less than or equal to the rotational speed ofthe fourth shaft. Thereby, there is always a linear relationship betweenthe rotational speeds of all four shafts.

Thereby, the rotational speed of one or more shafts also assume negativevalues, or even the value of zero. Therefore, the order of rotationalspeeds is always to refer to the signed value of the rotational speeds,and not to their amount.

The rotational speeds of the four shafts are equal if, of the elementsring gear, carrier and sun of one of the planetary gear sets, two ofsuch elements are connected to each other.

An electric motor consists at least of one torque-proof stator and onerotatably mounted rotor, and, during engine mode, is configured toconvert electrical energy into mechanical energy in the form ofrotational speed and torque, and, during generator mode, to convertmechanical energy into electrical energy in the form of current andvoltage.

Through shift elements, depending on their operating state, a relativemovement between two components is enabled, or a connection for thetransmission of a torque between the two components is established. A“relative movement” is understood as, for example, a rotation of twocomponents, whereas the rotational speed of the first component and therotational speed of the second component differ from each other. Inaddition, the rotation of only one of the two components is conceivable,while the other component is at a standstill or rotates in the oppositedirection. In the subject invention, the shift elements are preferablydesigned as claw-shift elements, which establish the connection by apositive connection.

Two elements are referred to as connected to each other particularly ifthere is a fixed (in particular, torque-proof) connection between theelements. Such connected elements rotate with the same rotational speed.The various components and elements of the specified invention may beconnected to each other through a shaft or through a locked shiftelement or a connection element, or also directly, for example by awelded connection, a crimping connection or another connection.

Furthermore, two elements are described as connectable if there is adetachably torque-proof connection between such elements. If theconnection exists, such elements rotate with the same rotational speed.

A shifting process is effected by locking a shift element of thetransmission that was previously not located in the power flow of thetransmission, and opening a shift element of the transmission previouslylocated in the power flow of the transmission. The shifting process mayalso be undertaken under load, that is without a complete withdrawal ofthe torque at the transmission input shaft and the transmission outputshaft. Such a shifting process is hereinafter referred to as a “loadshift.” With the use of claw-shift elements, a requirement for a loadshift is that the shift element to be released is guided into a statethat is at least nearly load-free prior to its release. The guiding intothe state that is nearly load-free is achieved by the fact that theshift element is made largely free of torque, such that, through theshift element, no torque or only a small torque is transferred. For thispurpose, through the electric motor, a torque is applied at that shaftwith which the shift element to be released establishes a connection.

In accordance with exemplary aspects of the invention, the second shaftof the auxiliary gear set is connectable through a first auxiliary shiftelement to the first shaft of the main gear set and through a secondauxiliary shift element to the third or fourth shafts of the main gearset. The third shaft of the auxiliary gear set is constantly connectedto the second shaft of the main gear set.

Thereby, either the first auxiliary shift element or the secondauxiliary shift element is locked. During a switchover phase between thefirst and second auxiliary shift elements, one of the auxiliary shiftelements is initially open, and the other auxiliary shift element isthen locked. Therefore, during this switchover phase, both of theauxiliary shift elements are never locked for a short period of time.

Through the first and second auxiliary shift element, the position ofthe first shaft of the auxiliary gear set in the rotational speeddiagram can be selectively influenced. If the first auxiliary shiftelement is locked and the second auxiliary shift element is open, thesecond shaft of the auxiliary gear set is connected to the first shaftof the main gear set. In this position of the first and second auxiliaryshift elements, the first shaft of the main gear set is located in therotational speed diagram between the first shaft of the auxiliary gearset and the second shaft of the main gear set. This case is hereinafterreferred to as the first operating state.

If the second auxiliary shift element is locked and the first auxiliaryshift element is open, the second shaft of the auxiliary gear set isconnected to the third or fourth shaft of the main gear set. This caseis hereinafter referred to as the second operating state. In thisposition of the first and second auxiliary shift element, the positionof the first shaft of the auxiliary gear set in the rotational speeddiagram changes compared to the first operating state. In the case inwhich the second shaft of the auxiliary gear set is connected throughthe locked second auxiliary shift element to the fourth shaft of themain gear set, the fourth shaft of the main gear set is located in therotational speed diagram between the third shaft of the main gear setand the first shaft of the auxiliary gear set. In the case in which thesecond shaft of the auxiliary gear set is connected through the lockedsecond auxiliary shift element to the third shaft of the main gear set,the position of the first shaft of the auxiliary gear set depends on thestationary transmission ratios of the first and second planetary gearsets of the main gear set and of the planetary gear set of the auxiliarygear set. Thereby, it is either the case that the fourth shaft of themain gear set is located in the rotational speed diagram between thethird shaft of the main gear set and the first shaft of the auxiliarygear set, or the first shaft of the auxiliary gear set is located in therotational speed diagram between the third and fourth shafts of the maingear set.

Through the arrangement in accordance with exemplary aspects of theinvention, it is achieved that, for the load release of the shiftelement upon the load-shifting process, the electric motor alwaysdelivers power rather than receives power. In other words, for the loadrelease of the shift element, the electric motor is always operated in amotor operating point rather than in a generator operating point. Thisconsiderably reduces the torque decline at the transmission output shaftduring the load-shifting process. Depending on the allocation of theshift elements at the shafts of the main gear set, in the engaged gear,either the first or the second operating state is occupied, such that,at least upon a gear shift to the next highest or next lower gear, thefirst shaft of the auxiliary gear set occupies the position in therotational speed diagram advantageous for this gear shift.

Through the arrangement in accordance with exemplary aspects of theinvention, it is also achieved that the rotor, even with a torque-prooffixing of one of the shafts of the main gear set, is able to assume arotational speed. The assumption of a rotational speed is a prerequisitefor the receiving and delivering of mechanical power by the electricmotor. It is thereby enabled that the electric motor is capable ofreceiving or delivering mechanical power in those gears in which, forexample, the first shaft of the main gear set is fixed in a torque-proofmanner or does not have an appreciable rotational speed. This isparticularly advantageous when using the transmission in a motorvehicle, since kinetic energy of the motor vehicle can be recuperated ineach gear of the transmission through the generator mode of the electricmotor. If an internal combustion engine is connected to the transmissioninput shaft, the load point of the internal combustion engine in such away can be displaced in any gear by the generator mode or engine mode ofthe electric motor. Thus, the transmission enables an increase inefficiency of the motor vehicle.

The two auxiliary shift elements preferably can be actuated by adouble-acting actuator. This reduces both the installation expenditureand the manufacturing costs of the transmission.

Preferably, a sun gear of the planetary gear set of the auxiliary gearset is a component of the first shaft of the auxiliary gear set. In theevent that the planetary gear set of the auxiliary gear set is formed asa negative gear set, a carrier of the planetary gear set of theauxiliary gear set is a component of the second shaft of the auxiliarygear set, and a ring gear of the planetary gear set of the auxiliarygear set is a component of the third shaft of the auxiliary gear set. Ifthe planetary gear set of the auxiliary gear set is formed as a positivegear set, the allocation of the ring gear and the carrier isinterchanged, such that the ring gear of the planetary gear set of theauxiliary gear set is a component of the second shaft of the auxiliarygear set, and the carrier of the planetary gear set of the auxiliarygear set is a component of the third shaft of the auxiliary gear set. Indoing so, the rotational speed of the second shaft of the auxiliary gearset is always between the rotational speeds of the first and thirdshafts of the auxiliary gear set, if the specified elements of theplanetary gear set of the auxiliary gear set do not circulate with thesame rotational speed.

Upon the use of a positive gear set, it must be taken into account thatthe amount of the fixed transmission ratio must be increased by thevalue of one in order to achieve the same transmission ratio effect as anegative gear set.

As such, through the multiple number of options offered for theconnection between the rotor, the auxiliary gear set and the main gearset, the invention in accordance with exemplary aspects of isparticularly easily adjustable for various transmission variants andavailable installation space ratios.

The sequence of the four shafts of the main gear set in the rotationalspeed diagram depends on the manner in which shafts are allocated towhich elements of the first and second planetary gear sets of the maingear set, and which of the four shafts are connected to each other.Examples of this are known in the state of the art, but certain variantshave emerged as particularly advantageous for implementation in atransmission. These are particularly advantageous based on ageometrically favorable arrangement, based on reduced component stressand based on improved accessibility to the shift elements.

According to a preferred variant, the first shaft of the main gear setis connected to a sun gear of the first planetary gear set of the maingear set. The second shaft of the main gear set is connected to acarrier of the first planetary gear set and a ring gear of the secondplanetary gear set of the main gear set. The third shaft of the maingear set is connected to a ring gear of the first planetary gear set andto a carrier of the second planetary gear set of the main gear set. Thefourth shaft of the main gear set is connected to a sun gear of thesecond planetary gear set of the main gear set. Thereby, the first andsecond planetary gear sets are formed as negative gear sets.

The transmission in accordance with exemplary aspects of the inventionis preferably formed as a load-shiftable eight-speed transmission. Thiseight-speed transmission features a first power path and a second powerpath between the transmission input shaft and the main gear set.Thereby, the first and second power paths feature different transmissionratios for the transmission input shaft. The first power path isconnected through a first shift element to the fourth shaft of the maingear set and through a second shift element to the second shaft of themain gear set. The second power path is connected through a third shiftelement to the first shaft of the main gear set and through a fourthshift element to the second shaft of the main gear set. The first shaftof the main gear set can be fixed in a torque-proof manner through afifth shift element. The fourth shaft of the main gear set can be fixedin a torque-proof manner through a sixth shift element. Accordingly,through the fifth and sixth shift elements, a firm connection to atransmission housing of the transmission, or to a different component ofthe transmission that is fixed in a torque-proof manner, can beestablished. This arrangement of the first to sixth shift elementsresults in a particularly advantageous allocation of the individualgears.

Through the selective meshing in pairs of the first to sixth shiftelements, eight forward gears can be realized between the transmissioninput shaft and the transmission output shaft. A first forward geararises from the locking of the third shift element and the sixth shiftelement. A second forward gear arises from the locking of the fourthshift element and the sixth shift element. A third forward gear arisesfrom the locking of the third shift element and the fourth shiftelement. A fourth forward gear arises from the locking of the fourthshift element and the first shift element. A fifth forward gear arisesfrom the locking of the third shift element and the first shift element.A sixth forward gear arises from the locking of the second shift elementand the first shift element. A seventh forward gear arises from thelocking of the third shift element and the second shift element. Aneighth forward gear arises from the locking of the fifth shift elementand the second shift element.

With the load-shiftable eight-speed transmission described above, in thefirst, fifth and eighth forward gears, the transmission preferablyoccupies the first operating state. In the third forward gear, thetransmission preferably occupies the second operating state. In thesecond, fourth, sixth and seventh forward gears, there is preferably aswitch from the first operating state to the second operating state, orvice versa.

According to a preferred exemplary embodiment of the eight-speedtransmission, two shift elements can be actuated by a double-actingactuator. The third and fifth shift elements can be actuated by a firstdouble-acting actuator. The second and fourth shift elements can beactuated by a second double-acting actuator. The first and sixth shiftelements can be actuated by a third double-acting actuator. Each of thethree double-acting actuators may occupy three states. In a firstshifting state of the double-acting actuator, the first shift elementallocated to the actuator is in a locked position, while the secondshift element allocated to the actuator occupies an open position. In asecond shifting state of the actuator, the second shift elementallocated to the actuator is in a locked position, while the first shiftelement allocated to the actuator occupies an open position. In a thirdshifting state, both shift elements allocated to the actuator occupy theopen position. Based on the design of the main gear set and theconnection of the main gear set to the electric motor, this allocationof the first to sixth shift elements to only three double-actingactuators is enabled. This reduced number of actuators helps to reducethe complexity of the transmission, and reduces the manufacturing costsof the transmission.

Preferably, the transmission may be a component of a hybrid drive trainof a motor vehicle. The hybrid drive train features an internalcombustion engine, in addition to the transmission. The internalcombustion engine is connected or connectable, either directly orthrough a clutch, to the transmission input shaft of the transmission.The motor vehicle may be driven by both the internal combustion engineand the electric motor of the transmission. Optionally, the hybrid drivetrain features an auxiliary electric motor, which is configured to,through its rotor, deliver torque to the crankshaft of the internalcombustion engine and, in such a way, start the internal combustionengine. This has the advantage that the internal combustion engine canbe started by the auxiliary electric motor, without having any influenceon a simultaneous electric driving mode, by the motor vehicle beingdriven solely by the electric motor of the transmission. If the hybriddrive train features a clutch between the transmission and the internalcombustion engine and an auxiliary electric motor, the auxiliaryelectric motor is preferably arranged in the power flow between theinternal combustion engine and the clutch. The clutch may feature avariable torque transfer capacity.

The electric motor is connected to a converter, through which theelectric motor is connected to an energy storage device. For thispurpose, any form of energy storage device (in particular, anelectrochemical, electrostatic, hydraulic or mechanical energy storagedevice) is suitable.

In an additional exemplary embodiment, the transmission may also be acomponent of a drive train of an electric motor vehicle. An electricmotor vehicle is driven solely by one or more electric motors, andaccordingly has no internal combustion engine. In this case, a tractionelectric motor is connected to the transmission input shaft. Through thedifferent transmission ratio stages of the transmission, the tractionelectric motor may always be operated in an operating range with a highdegree of efficiency, by which the energy efficiency of the entireelectric motor vehicle is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are described in detail on thebasis of the attached figures.

FIG. 1 schematically shows a transmission in accordance with a firstexemplary embodiment of the invention.

FIG. 2 shows a rotational speed plan of the exemplary transmission.

FIG. 3 shows a shifting diagram of the exemplary transmission.

FIG. 4 schematically shows a transmission in accordance with a secondexemplary embodiment of the invention.

FIG. 5 shows a hybrid drive train of a motor vehicle.

FIG. 5a shows another embodiment of a hybrid drive train of a motorvehicle.

DETAILED DESCRIPTION

Reference will now be made to embodiments of the invention, one or moreexamples of which are shown in the drawings. Each embodiment is providedby way of explanation of the invention, and not as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be combined with another embodiment to yield stillanother embodiment. It is intended that the present invention includethese and other modifications and variations to the embodimentsdescribed herein.

At the outset, it must be stated that, in the various describedembodiments, the same parts are provided with the same reference signsor the same component names, whereby the disclosures containedthroughout the description can be transferred analogously to the sameparts with the same reference signs or the same component names.

FIG. 1 schematically shows a transmission G in accordance with a firstexemplary embodiment of the invention. The transmission G features anupstream gear set VRS, an auxiliary gear set ZRS and a main gear setHRS. The upstream gear set VRS features a planetary gear set P3, and theauxiliary gear set ZRS features a planetary gear set P4. while the maingear HRS features a first planetary gear set P1 and a second planetarygear set P2. All planetary gear sets P1, P2, P3, P4 are formed asnegative gear sets.

The presentation of the transmission G essentially shows the connectableand connected elements of the transmission G. Conclusions regarding thetransmission ratio relationships cannot be drawn by the distancesselected in the presentation of the transmission G.

A transmission input shaft GW1 is connected to a sun gear So-P3 of theplanetary gear set P3 of the upstream gear set VRS, while a ring gearHo-P3 of the planetary gear set P3 of the upstream gear set VRS isconnected in a torque-proof manner to the transmission housing GG of thetransmission G, or to a different component of the transmission G thatis fixed in a torque-proof manner. In such a way, a first and a secondpower path L1, L2 are formed, whereas power from the transmission inputshaft GW1 can be transferred to the main gear set HRS through both thefirst power path L1 and through the second power path L2. The secondpower path L2 thereby transmits to the main gear set HRS a rotationalspeed that is changed compared to the rotational speed of thetransmission input shaft GW1, by translating the rotational speed at thetransmission input shaft GW1 by the transmission ratio between the sungear So-P3 and a carrier St-P3 of the planetary gear set P3 of theupstream gear set VRS. The first power path L1 transmits the rotationalspeed of the transmission input shaft GW1 without a transmission ratioto the main gear set HRS. Thereby, the sun gear So-P3 of the planetarygear set P3 of the upstream gear set VRS is a component of a first shaftW1VS of the upstream gear set VRS, which is connected to thetransmission input shaft GW1. The carrier St-P3 of the planetary gearset P3 of the upstream gear set VRS is a component of a second shaftW2VS of the upstream gear set VRS. That component on which the ring gearHo-P3 of the planetary gear set P3 of the upstream gear set VRS issupported is referred to below as the third shaft W3VS of the upstreamgear set VRS.

A first shaft W1 of the main gear set HRS is connected to a sun gearSo-P1 of the first planetary gear set P1 of the main gear set HRS. Asecond shaft W2 of the main gear set HRS is connected to a carrier St-P1of the first planetary gear set P1 and to a ring gear Ho-P2 of thesecond planetary gear set P2 of the main gear set HRS. A third shaft W3of the main gear set HRS is connected to a ring gear Ho-P1 of the firstplanetary gear set P1 and to a carrier St-P2 of the second planetarygear set P2 of the main gear set HRS. A fourth shaft W4 of the main gearset HRS is connected to a sun gear So-P2 of the second planetary gearset P2 of the main gear set HRS. Through this arrangement and connectionbetween the individual components of the first and second planetary gearsets P1, P2 of the main gear set HRS, the arrangement of the first,second, third and fourth shafts W1, W2, W3, W4 of the main gear set HRSin the rotational speed diagram is determined, whereas the sequence offirst, second, third, fourth shafts W1, W2, W3, W4 corresponds to theirsequence in the rotational speed diagram. The third shaft W3 isconnected to a transmission output shaft GW2. Alternatively, the thirdshaft W3 may also be connected through an additional transmissiongearing to the transmission output shaft GW2. Thereby, the sun gearSo-P2 of the second planetary gear set P2 of the main gear set HRSfeatures two parts that are separate from each other. This facilitatesthe connection of the transmission output shaft GW2 to the third shaftW3 of the main gear set HRS, which is arranged between the two parts ofthe sun gear So-P2. Of course, the rotational speed relationships arethe same on both parts of the sun gear So-P2. Consequently, hereinafter,both parts of the sun gear So-P2 are referred to as one component of thesame shaft, specifically the fourth shaft W4 of the main gear set HRS.In an alternative exemplary embodiment that is not shown for reasons ofclarity, the sun gear So-P2 of the second planetary gear set P2 of themain gear set HRS may also be designed in one piece, for example, in thecase of a use of the transmission in the motor vehicle, in a drive trainarranged in a manner transverse to the direction of travel, whereas, inthis case, the transmission G has an axially parallel output.

The first power path L1 is connectable through a first shift element Ato the fourth shaft W4 of the main gear set HRS and through a secondshift element E to the second shaft W2 of the main gear set HRS. Thesecond power path L2 is connectable through a third shift element B tothe first shaft W1 of the main gear set HRS and through a fourth shiftelement D to the second shaft W2 of the main gear set HRS. The firstshaft W1 of the main gear set HRS is connectable through a fifth shiftelement C to the transmission housing GG of the transmission G, or toanother torque-proof component of the transmission G, such that, with alocked fifth shift element C, the first shaft W1 of the main gear setHRS cannot assume any rotational speed. In the same manner, the fourthshaft W4 of the main gear set HRS can be fixed in a torque-proof mannerthrough a sixth shift element F, by connecting the fourth shaft W4through the sixth shift element F to the transmission housing GG.

In each case, two shift elements are actuated by a double-actingactuator. The third and fifth shift elements B, C can be actuated by afirst double-acting actuator. The second and fourth shift elements E, Dcan be actuated by a second double-acting actuator. The first and sixthshift elements A, F can be actuated by a third double-acting actuator.

The transmission G features an electric motor EM, whereas a stator S isconnected in a torque-proof manner to the transmission housing GG of thetransmission G or to another torque-proof component of the transmissionG, such that the stator S cannot assume any rotational speed. Arotatably mounted rotor R is connected to a sun gear So-P4 of theplanetary gear set P4 of the auxiliary gear set ZRS. The sun gear So-P4of the planetary gear set P4 of the auxiliary gear set ZRS is acomponent of a first shaft W1P4 of the auxiliary gear set ZRS. A carrierSt-P4 of the planetary gear set P4 of the auxiliary gear set ZRS is acomponent of a second shaft W2P4 of the auxiliary gear set ZRS. Thesecond shaft W2P4 of the auxiliary gear set ZRS is connectable through afirst auxiliary shift element U to the first shaft W1 of the main gearset HRS, and through a second auxiliary shift element V to the thirdshaft W3 of the main gear set HRS. A ring gear Ho-P4 of the planetarygear set P4 of the auxiliary gear set ZRS is a component of a thirdshaft W3P4 of the auxiliary gear set ZRS and is connected to the secondshaft W2 of the main gear set HRS.

FIG. 2 shows a rotational speed diagram of the transmission G, while ashifting diagram of the transmission G is shown in FIG. 3. In FIG. 2,the rotational speeds of the four shafts W1, W2, W3, W4 of the main gearset HRS and the first shaft W1P4 of the auxiliary gear set ZRS areplotted in a vertical direction in relation to the rotational speed n ofthe transmission input shaft GW1. The maximum arising rotational speed nof the transmission input shaft GW1 is normalized to the value of one.The distances between the four shafts W1, W2, W3, W4 of the main gearset HRS and the first shaft W1 P4 of the auxiliary gear set ZRS arisefrom the stationary transmission ratios of the first and secondplanetary gear sets P1, P2 of the main gear set HRS and the stationarytransmission ratio of the planetary gear set P4 of the auxiliary gearset ZRS. Rotational speed relationships pertaining to a given operatingpoint can be connected by a straight line.

If the first auxiliary shift element U is locked, the first shaft W1 ofthe main gear set HRS is located in the rotational speed diagram betweenthe first shaft W1P4 of the auxiliary gear set ZRS and the second shaftW2 of the main gear set HRS. If the second auxiliary shift element V islocked, the fourth shaft W4 of the main gear set HRS is located in therotational speed diagram between the third shaft W3 of the main gear setHRS and the first shaft W1 P4 of the auxiliary gear set ZRS.

If two shafts are connected to each other, such shafts connected to eachother rotate with the same rotational speed. For reasons of clarity,such connected shafts can be shown separated from each otherhorizontally in the rotational speed diagram, in order to, for example,better clarify the rotational speed transfer from the upstream gear setVRS through the first or second power paths L1, L2 to the main gear setHRS. The horizontal distance between the connected shafts that isthereby selected in the rotational speed diagram is arbitrary. Ofcourse, the transmission ratio between such connected shafts amounts tothe value of one, independent of the horizontal distance selected in therotational speed diagram.

If, of the ring gear, carrier and sun of a planetary gear set, two ofsuch elements are connected to each other, the ring gear, carrier andsun of such planetary gear set rotate with the same rotational speed. Inthis state, the transmission ratio relationship between the specifiedelements assumes the value of one. For reasons of clarity, thehorizontal arrangement of the shafts connected to such elements is notshifted in the rotational speed diagram. Consequently, this conditioncan be seen in the rotational speed diagram by a horizontal straightline, which connects the participating shafts to each other.

FIG. 3 shows a shifting diagram of the transmission G in accordance withthe first exemplary embodiment. Through the shifting diagram in FIG. 3and the rotational speed diagram in FIG. 2, the operation of thetransmission G becomes clear. The locked shift elements A, B, C, D, E, Fand the auxiliary shift elements U, V are indicated by circles in FIG.3. By way of example, the respective transmission ratios of theindividual gear steps and the gear jumps to the next higher gear to bedetermined from them may be taken from the shifting diagram, whereas thetransmission G in such a way has a spread of 10.1. The transmissionratios arise from the stationary transmission ratios of the planetarygear sets P1, P2, P3, P4. Upon a sequential shifting operation, doublegearshifts and group gearshifts can be avoided, since two adjacent gearsteps jointly use one shift element. The gears of the transmission G areshown in the various lines of the shifting diagram. One column of theshifting diagram further indicates whether the electric motor EM in therelevant gear is able to deliver mechanical power to the transmissionoutput shaft GW2, or receive mechanical power from it.

A first forward gear 1VM between the transmission input shaft GW1 andthe transmission output shaft GW2 arises from the locking of the thirdshift element B and the sixth shift element F, a second forward gear 2VMarises from the locking of the fourth shift element D and the sixthshift element F, a third forward gear 3VM arises from the locking of thethird shift element B and the fourth shift element D, a fourth forwardgear 4VM arises from the locking of the fourth shift element D and thefirst shift element A, a fifth forward gear 5VM arises from the lockingof the third shift element B and the first shift element A, a sixthforward gear 6VM arises from the locking of the second shift element Eand the first shift element A, a seventh forward gear 7VM arises fromthe locking of the third shift element B and the second shift element E,and an eighth forward gear 8VM arises from the locking of the fifthshift element C and the second shift element E.

In the first, fifth and eighth forward gears 1VM, 5VM, 8VM, the firstauxiliary shift element U is locked. In the third forward gear 3VM, thesecond auxiliary shift element V is locked. In the second, fourth, sixthand seventh forward gears 2VM, 4VM, 6VM, 7VM, the first auxiliary shiftelement U is open and the second auxiliary shift element V is locked,and vice versa. In principle, however, the first or second auxiliaryshift elements U, V may be locked in all gears.

In a first electrical gear 1EM, torque is transferred solely from theelectric motor EM to transmission output shaft GW2, whereas the first,second, third, fourth shift elements A, E, B, D are open and there isthus no torque-transferring connection between the transmission inputshaft GW1 and the transmission output shaft GW2. The first auxiliaryshift element U and the sixth shift element F are locked. The fifthshift element C is open. In a second electrical gear 2EM, instead of thefirst auxiliary shift element U, the second auxiliary shift element V islocked. In the second electric gear 2EM, the sixth shift element F isopen and the fifth shift element C is locked.

In a first and second start mode 1S, 2S, torque is supplied to thetransmission input shaft GW1, whereas, depending on the position of thesixth shift element F, torque can be supplied to the transmission inputshaft GW1 exclusively by the electric motor EM or by the transmissionoutput shaft GW2. If the sixth shift element F is locked, and theelectric motor EM does not deliver any torque, the transmission inputshaft GW1 may also be supplied with torque exclusively by thetransmission output shaft GW2. This is particularly relevant when usingthe transmission G in a motor vehicle, in order to, in such a way, startan internal combustion engine VKM connected to the transmission inputshaft GW1. If the sixth shift element F is thereby open, thetransmission output shaft GW2 must be fixed in a torque-proof manner bya parking brake. The first auxiliary shift element U is locked.

In the following, a load-shifting process is described by way ofexample. In the second forward gear, each of the second and the fourthshafts W2, W4 of the main gear set HRS forms a differential shaft, whilethe third shaft W3 of the main gear set HRS represents a sum shaft. Upona shifting process from the second forward gear 2VM to the third forwardgear 3VM, the fourth shift element D is locked. During this shiftingprocess, the second auxiliary shift element V is preferably locked. Thesixth shift element F is open; the third shift element B is subsequentlylocked. If the sixth shift element F is formed as claw-shift element,the sixth shift element F must be made largely free of torque prior toopening, such that the sixth shift element F only transfers no torque orlow torque. This load release of the sixth shift element F is effectedby an engine torque of the electric motor EM. Thereby, at least oneportion of the torque previously applied at the third shaft W3 of themain gear set HRS is maintained, by which a complete loss of torque doesnot arise at the transmission output shaft GW2. If the sixth shiftelement F is open, the second shaft W2 of the main gear set HRS becomesthe sum shaft, while each of the first shaft W1P4 of the auxiliary gearset ZRS and the third shaft W3 of the main gear set HRS forms adifferential shaft. Through the electric motor EM, an engine torque isnow applied, in order to achieve a synchronization of rotational speedsbetween the second shaft W2VS of the upstream gear set VRS and the firstshaft W1 of the main gear set HRS. This enables a locking of the thirdshift element B, whereas at least one portion of the torque previouslyapplied at the third shaft W3 of the main gear set HRS is maintained. Ifthe third shift element B is locked, the first shaft W1 of the main gearset HRS becomes the differential shaft; the shifting process is thuscompleted. This mode of operation applies to all embodiments.

FIG. 4 schematically shows a transmission G in accordance with a secondexemplary embodiment of the invention. In contrast to the firstexemplary embodiment, the second shaft W2P4 of the auxiliary gear setZRS through the second auxiliary shift element V is now no longerconnectable to the third shaft W3 of the main gear set HRS. Instead, thesecond shaft W2P4 of the auxiliary gear set ZRS is now connectablethrough the second auxiliary shift element V to the fourth shaft W4 ofthe main gear set HRS. The rotational speed diagram described in FIG. 2and the shifting diagram described in FIG. 3 apply in the same form tothe second exemplary embodiment of the transmission G, to the extentthat the stationary transmission ratios of the participating planetarygear sets P1, P2, P4 are selected accordingly.

FIG. 5 schematically shows a hybrid drive train of a motor vehicle. Thetransmission G contained therein corresponds to the first exemplaryembodiment of the transmission G, whereas this is to be regarded merelyas an example. A rotatable rotor R2 of an auxiliary electric motor SG isconnected to the transmission input shaft GW1, while the stator S2 ofthe auxiliary electric motor SG is fixed in a torque-proof manner to thetransmission housing GG of the transmission G or to another torque-proofcomponent of the transmission G. Through a rotational vibration damperRD, an internal combustion engine VKM is connected to the transmissioninput shaft GW1. The transmission output shaft GW2 is connected to anaxle drive AG. Starting from the axle drive AG, the torque that appliesat the transmission output shaft GW2 is distributed to wheels W of themotor vehicle. In engine mode of the electric motor EM, electric poweris supplied to the stator S through a power inverter INV. In generatormode of the electric motor EM, the stator S supplies electric power tothe power inverter INV. Thereby, the power inverter INV converts the DCvoltage of a battery BAT into an AC voltage suitable for the electricmotor EM, and vice versa. Thereby, the auxiliary electric motor SG maylikewise be supplied with electric power through the power inverter INV.Alternatively, the auxiliary electric motor SG may also be connected toa different power supply, for example, to a low-voltage electricalsystem of the motor vehicle.

FIG. 5a schematically shows a hybrid transmission of a motor vehicle.The embodiment shown in FIG. 5a differs from the embodiment shown inFIG. 5 in that there is a clutch K0 between the transmission G and theinternal combustion engine VKM, where the auxiliary electric motor SG isarranged in the power flow between the internal combustion engine VKMand the clutch K0. The clutch K0 may feature a variable torque transfercapacity.

Modifications and variations can be made to the embodiments illustratedor described herein without departing from the scope and spirit of theinvention as set forth in the appended claims.

REFERENCE SIGNS

-   G Transmission-   GW1 Transmission input shaft-   GW2 Transmission output shaft-   n Rotational speed of the transmission input shaft-   HRS Main gear set-   ZRS Auxiliary gear set-   VRS Upstream gear set-   EM Electric motor-   R Rotor of the electric motor-   S Stator of the electric motor-   SG Auxiliary electric motor-   R2 Rotor of the auxiliary electric motor-   R2 Stator of the auxiliary electric motor-   RD Rotational vibration damper-   VKM Internal combustion engine-   INV Power inverter-   BAT Battery-   K0 Clutch-   P1 First planetary gear set of the main gear set-   P2 Second planetary gear set of the main gear set-   P3 Planetary gear set of the upstream gear set-   P4 Planetary gear set of the auxiliary gear set-   W1 First shaft of the main gear set-   W2 Second shaft of the main gear set-   W3 Third shaft of the main gear set-   W4 Fourth shaft of the main gear set-   W1VS First shaft of the upstream gear set-   W2VS Second shaft of the upstream gear set-   W3VS Third shaft of the upstream gear set-   W1P4 First shaft of the auxiliary gear set-   W2P4 Second shaft of the auxiliary gear set-   W3P4 Third shaft of the auxiliary gear set-   A First shift element-   E Second shift element-   B Third shift element-   D Fourth shift element-   C Fifth shift element-   F Sixth shift element-   U First auxiliary shift element-   V Second auxiliary shift element-   So-P1 Sun gear of the first planetary gear set of the main gear set-   St-P1 Carrier of the first planetary gear set of the main gear set-   Ho-P1 Ring gear of the first planetary gear set of the main gear set-   So-P2 Sun gear of the second planetary gear set of the main gear set-   St-P2 Carrier of the second planetary gear set of the main gear set-   Ho-P2 Ring gear of the second planetary gear set of the main gear    set-   So-P3 Sun gear of the planetary gear set of the upstream gear set-   St-P3 Carrier of the planetary gear set of the upstream gear set-   Ho-P3 Ring gear of the planetary gear set of the upstream gear set-   So-P4 Sun gear of the planetary gear set of the auxiliary gear set-   St-P4 Carrier of the planetary gear set of the auxiliary gear set-   Ho-P4 Ring gear of the planetary gear set of the auxiliary gear set-   L1 First power path-   L2 Second power path-   1VM-8VM First to eighth forward gears-   1EM First electric gear-   2EM Second electric gear-   1S First start mode-   2S Second start mode-   AG Axle drive-   W Wheel

The invention claimed is:
 1. A transmission, comprising a transmissioninput shaft; a transmission output shaft; a plurality of shift elements;a main gear set, at least one power path formable between thetransmission input shaft and the main gear set, the main gear setcomprising a first planetary gear set, a second planetary gear set andfour shafts, the at least one power path connectable through at leastone shift element of the plurality of shift elements to at least one ofthe four shafts of the main gear set, a third shaft of the main gear setis connected to the transmission output shaft; an auxiliary gear setcomprising a planetary gear set and three shafts, a second shaft of theauxiliary gear set connectable through a first auxiliary shift elementto a first shaft of the main gear set, the second shaft of the auxiliarygear set connectable through a second auxiliary shift element to thethird shaft of the main gear set or to a fourth shaft of the main gearset, a third shaft of the auxiliary gear set is constantly connected toa second shaft of the main gear set; and an electric motor with a rotorand a stator, a first shaft of the auxiliary gear set is constantlyconnected to the rotor, wherein either the first auxiliary shift elementor the second auxiliary shift element is locked during operation of thetransmission, and wherein the four shafts of the main gear set aredesignated in order of rotational speed as the first, second, third andfourth shafts such that there is a linear rotational speed relationshipbetween the first, second, third and fourth shafts.
 2. The transmissionof claim 1, wherein; a sun gear of the planetary gear set of theauxiliary gear set is a component of the first shaft of the auxiliarygear set; when the planetary gear set of the auxiliary gear set is anegative gear set, a carrier of the planetary gear set of the auxiliarygear set is a component of the second shaft of the auxiliary gear set,and a ring gear of the planetary gear set of the auxiliary gear set is acomponent of the third shaft of the auxiliary gear set; and when theplanetary gear set of the auxiliary gear set is a positive gear set, thering gear of the planetary gear set of the auxiliary gear set is acomponent of the second shaft of the auxiliary gear set, and the carrierof the planetary gear set of the auxiliary gear set is a component ofthe third shaft of the auxiliary gear set.
 3. The transmission of claim1, wherein a sun gear of the first planetary gear set of the main gearset is a component of the first shaft of the main gear set, a carrier ofthe first planetary gear set of the main gear set and a ring gear of thesecond planetary gear set of the main gear set are components of thesecond shaft of the main gear set, a ring gear of the first planetarygear set of the main gear set and a carrier of the second planetary gearset of the main gear set are components of the third shaft of the maingear set, and a sun gear of the second planetary gear set of the maingear set is a component of the fourth shaft of the main gear set.
 4. Thetransmission of claim 1, wherein the first auxiliary shift element andthe second auxiliary shift element are actuatable by a double-actingactuator.
 5. The transmission of claim 1, wherein the at least one powerpath includes a first power path and a second power path between thetransmission input shaft and the main gear set, the first power pathconnectable through a first shift element of the plurality of shiftelements to the fourth shaft of the main gear set, the first power pathconnectable through a second shift element of the plurality of shiftelements to the second shaft of the main gear set, the second power pathconnectable through a third shift element of the plurality of shiftelements to the first shaft of the main gear set, the second power pathconnectable through a fourth shift element of the plurality of shiftelements to the second shaft of the main gear set, the first shaft ofthe main gear set fixable in a torque-proof manner through a fifth shiftelement of the plurality of shift elements, the fourth shaft of the maingear set fixable in a torque-proof manner through a sixth shift elementof the plurality of shift elements.
 6. The transmission of claim 5,wherein: eight forward gears are realizable through selective locking ofthe plurality of shift elements in pairs; a first forward gear arisesfrom locking of the third shift element and the sixth shift element; asecond forward gear arises from locking of the fourth shift element andthe sixth shift element; a third forward gear arises from the locking ofthe third shift element and the fourth shift element; a fourth forwardgear arises from the locking of the fourth shift element and the firstshift element; a fifth forward gear arises from the locking of the thirdshift element and the first shift element; a sixth forward gear arisesfrom the locking of the second shift element and the first shiftelement; a seventh forward gear arises from the locking of the thirdshift element and the second shift element; and an eighth forward geararises from the locking of the fifth shift element and the second shiftelement.
 7. The transmission of claim 6, wherein the first auxiliaryshift element is locked at least in the first forward gear, in the fifthforward gear and in the eighth forward gear.
 8. The transmission ofclaim 6, wherein the second auxiliary shift element is locked at leastin the third forward gear.
 9. The transmission of claim 6, wherein: aswitchover process is realizable between a first operating state and asecond operating state in the second, fourth, sixth and seventh forwardgears; in the first operating state, the first auxiliary shift elementis locked and the second auxiliary shift element is open; in the secondoperating state, the second auxiliary shift element is locked and thefirst auxiliary shift element is open.
 10. The transmission of claim 5,wherein the third and fifth shift elements are actuatable by a firstdouble-acting actuator, the second and fourth shift elements areactuatable by a second double-acting actuator, and the first and sixthshift elements are actuatable by a third double-acting actuator.
 11. Ahybrid drive train for a motor vehicle, comprising at least one internalcombustion engine and the transmission of claim
 1. 12. The hybrid drivetrain of claim 11, further comprising at least one auxiliary electricmotor connected to the internal combustion engine directly or throughthe transmission, the at least one auxiliary electric motor operable tostart the internal combustion engine.
 13. The hybrid drive train ofclaim 11, further comprising a clutch operable to interrupt power flowbetween the internal combustion engine and the transmission input shaft.14. A drive train for an electric vehicle, comprising the transmissionof claim 1.